terraform/vendor/github.com/Azure/azure-sdk-for-go/management/http.go

package management

import (
	"bytes"
	"crypto/tls"
	"fmt"
	"net/http"
)

const (
	msVersionHeader           = "x-ms-version"
	requestIDHeader           = "x-ms-request-id"
	uaHeader                  = "User-Agent"
	contentHeader             = "Content-Type"
	defaultContentHeaderValue = "application/xml"
)

func (client client) SendAzureGetRequest(url string) ([]byte, error) {
	resp, err := client.sendAzureRequest("GET", url, "", nil)
	if err != nil {
		return nil, err
	}
	return getResponseBody(resp)
}

func (client client) SendAzurePostRequest(url string, data []byte) (OperationID, error) {
	return client.doAzureOperation("POST", url, "", data)
}

func (client client) SendAzurePostRequestWithReturnedResponse(url string, data []byte) ([]byte, error) {
	resp, err := client.sendAzureRequest("POST", url, "", data)
	if err != nil {
		return nil, err
	}

	return getResponseBody(resp)
}

func (client client) SendAzurePutRequest(url, contentType string, data []byte) (OperationID, error) {
	return client.doAzureOperation("PUT", url, contentType, data)
}

func (client client) SendAzureDeleteRequest(url string) (OperationID, error) {
	return client.doAzureOperation("DELETE", url, "", nil)
}

func (client client) doAzureOperation(method, url, contentType string, data []byte) (OperationID, error) {
	response, err := client.sendAzureRequest(method, url, contentType, data)
	if err != nil {
		return "", err
	}
	return getOperationID(response)
}

func getOperationID(response *http.Response) (OperationID, error) {
	requestID := response.Header.Get(requestIDHeader)
	if requestID == "" {
		return "", fmt.Errorf("Could not retrieve operation id from %q header", requestIDHeader)
	}
	return OperationID(requestID), nil
}

// sendAzureRequest constructs an HTTP client for the request, sends it to the
// management API and returns the response or an error.
func (client client) sendAzureRequest(method, url, contentType string, data []byte) (*http.Response, error) {
	if method == "" {
		return nil, fmt.Errorf(errParamNotSpecified, "method")
	}
	if url == "" {
		return nil, fmt.Errorf(errParamNotSpecified, "url")
	}

	httpClient, err := client.createHTTPClient()
	if err != nil {
		return nil, err
	}

	response, err := client.sendRequest(httpClient, url, method, contentType, data, 5)
	if err != nil {
		return nil, err
	}

	return response, nil
}

// createHTTPClient creates an HTTP Client configured with the key pair for
// the subscription for this client.
func (client client) createHTTPClient() (*http.Client, error) {
	cert, err := tls.X509KeyPair(client.publishSettings.SubscriptionCert, client.publishSettings.SubscriptionKey)
	if err != nil {
		return nil, err
	}

	return &http.Client{
		Transport: &http.Transport{
			Proxy: http.ProxyFromEnvironment,
			TLSClientConfig: &tls.Config{
				Renegotiation: tls.RenegotiateOnceAsClient,
				Certificates:  []tls.Certificate{cert},
			},
		},
	}, nil
}

// sendRequest sends a request to the Azure management API using the given
// HTTP client and parameters. It returns the response from the call or an
// error.
func (client client) sendRequest(httpClient *http.Client, url, requestType, contentType string, data []byte, numberOfRetries int) (*http.Response, error) {

	absURI := client.createAzureRequestURI(url)

	for {
		request, reqErr := client.createAzureRequest(absURI, requestType, contentType, data)
		if reqErr != nil {
			return nil, reqErr
		}

		response, err := httpClient.Do(request)
		if err != nil {
			if numberOfRetries == 0 {
				return nil, err
			}

			return client.sendRequest(httpClient, url, requestType, contentType, data, numberOfRetries-1)
		}
		if response.StatusCode == http.StatusTemporaryRedirect {
			// ASM's way of moving traffic around, see https://msdn.microsoft.com/en-us/library/azure/ee460801.aspx
			// Only handled automatically for GET/HEAD requests. This is for the rest of the http verbs.
			u, err := response.Location()
			if err != nil {
				return response, fmt.Errorf("Redirect requested but location header could not be retrieved: %v", err)
			}
			absURI = u.String()
			continue // re-issue request
		}

		if response.StatusCode >= http.StatusBadRequest {
			body, err := getResponseBody(response)
			if err != nil {
				// Failed to read the response body
				return nil, err
			}
			azureErr := getAzureError(body)
			if azureErr != nil {
				if numberOfRetries == 0 {
					return nil, azureErr
				}

				return client.sendRequest(httpClient, url, requestType, contentType, data, numberOfRetries-1)
			}
		}

		return response, nil
	}
}

// createAzureRequestURI constructs the request uri using the management API endpoint and
// subscription ID associated with the client.
func (client client) createAzureRequestURI(url string) string {
	return fmt.Sprintf("%s/%s/%s", client.config.ManagementURL, client.publishSettings.SubscriptionID, url)
}

// createAzureRequest packages up the request with the correct set of headers and returns
// the request object or an error.
func (client client) createAzureRequest(url string, requestType string, contentType string, data []byte) (*http.Request, error) {
	var request *http.Request
	var err error

	if data != nil {
		body := bytes.NewBuffer(data)
		request, err = http.NewRequest(requestType, url, body)
	} else {
		request, err = http.NewRequest(requestType, url, nil)
	}

	if err != nil {
		return nil, err
	}

	request.Header.Set(msVersionHeader, client.config.APIVersion)
	request.Header.Set(uaHeader, client.config.UserAgent)

	if contentType != "" {
		request.Header.Set(contentHeader, contentType)
	} else {
		request.Header.Set(contentHeader, defaultContentHeaderValue)
	}

	return request, nil
}